Nicotine is a highly addictive substance, and nicotine dependence results in major public health costs. Nicotine acts on specific receptors in the brain, neuronal nicotinic receptors, whose physiological properties and role in the brain are not well understood. The proposed work will examine the pharmacology and physiology of a major class of human brain receptors, composed of alpha 4 and beta 2 subunits. The overall goal is to define fundamental properties of these receptors, including basic properties of activation and desensitization, and the actions of specific drugs. To provide a defined population of receptors, the work will use receptors expressed in non-neural cells, either transiently or stably. The aims of the work are, first, to define the mechanisms by which some drugs potentiate the function of these receptors. The second aim is to define the mechanisms by which selected drugs block the function of these receptors. The third aim is to characterize desensitization of these receptors, including very low concentrations of nicotine. The final aim is to define the signal, which elicits an increase in the expression of these receptors. The first two aims will provide essential information about the actions of several drugs, including some in clinical use. The third aim will increase our understanding of the regulation of receptor activity by long-term exposure to nicotine and other drugs, including concentrations, which are reached in the brain of smokers. The final aim will use the insights gained in the previous work to gain an understanding of the mechanism by which ceils can increase the numbers of these receptors which they express on their surface. In addition to the actions of nicotine itself, drugs which act on nicotinic receptors are being used or proposed for use in treating a number of disorders, including Alzheimer's disease, attention deficit disorder and pain. Our understanding of the actions of these drugs is hampered our lack of knowledge about the mechanisms of their effects on the target nicotinic receptors. Furthermore, it is known that decreases in the expression of the alpha 4 beta 2 receptor are associated with some disorders, so increased understanding of the nature of the signal for upregulation may provide insights into these disorders and, possibly, therapeutic approaches. Overall, the proposed work will examine basic properties of receptors, to reach a greater understanding of receptor function and pharmacology, which can be applied to understanding the role of these receptors in normal and pathological brain function.